<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>下拉样式的输入框</title>
<style>
select {
    width: 100%;
    padding: 16px 20px;
    border: none;
    border-radius: 4px;
    background-color: #f1f1f1;
}
</style>
</head>
<body>
    <p>下拉菜单</p>
    <form>
        <select id="国家" name="国家">
        <option value="中国">中国</option>
        <option value="美国">美国</option>
        <option value="日本">日本</option>
        </select>
        </form>
</body>
</html>